Magnetohydrodynamic transformer



April 20, 1965 o. M. STUETZER MAGNETOHYDRODYNAMIC TRANSFORMER 2 Sheets-Sheet 1 Filed April 17, 1962 INVENTOR. OTMAR M. STUETZER BY 72 Z ATTORNEY A ril 20, 1965 o. M. STUETZER 3,179,324

MAGNETOHYDRODYNAMIC TRANSFORMER Filed April 17, 1962 2 Sheets-Sheet 2 INVEN TOR. OTMAR M- STUETZER Hw /w ATTORNEY United States Patent 3179,824 MAGNETOHYDRODYNAMIC TRANSFORMER Otmar M. Stuetzer, Hopkins, Minn., assignor, by mesne assignments, to Litton Systems, Inc., Beverly Hills,

Califi, a corporation of Maryland Filed Apr. 17, 1962, Ser. No. 188,103 3 Claims. (Cl. 310-11) Tln's invention relates to electrical transformers, and, more particularly, to a direct current transformer which operates on the principle of magnetohydrodynamics.

Heretofore, there has been no practical device available for transforming direct currents and voltages to other values. Consequently, it has been necessary to employ indirect or roundabout methods to achieve that end. One scheme that has been utilized involves electrically charging a plurality of capacitors connected in parallel, and then discharging the capacitors in series. This requires the use of commutator or switching arrangements and, furthermore, provides a pulsating direct current that must be smoothed or averaged out. Another method that has been utilized is to convert the direct current to alternating current, pass the alternating current through a transformer, and then reconvert the alternating current to direct current. This, of course, is expensive and cumbersome. The present invention provides means for transforming direct currents and voltages which obviate the disadvantages of the methods that have been necessarily used heretofore. It provides a direct current transformer, which is based on the principles of magnetohydrodynamics, and, because it has extremely low impedance, is particularly adapted for low voltage, high current applications.

Magnetohydrodynamics is that field of science which deals with the reactions induced in an electrically conductive fluid in the presence of a magnetic field. It is, in effect, a union of two branches of physical science, one dealing with fluid flow and the other with electromagnetic fields. For a theoretical treatment of the phenomena of magnetohydrodynamics, reference is made to a book entitled Magnetohydrodynamics by R. K. M. Landshoff, Stanford University Press, 1957, and to a book entitled Magnetohydrodynamics by T. G. Cowling, Interscience Publishers, Inc., New York, N.Y., 1957. In addition, many scientific and technical papers have been published on the subject within the last several years.

It is known that if a highly conductive fluid is placed in a magnetic field and current is passed through the fluid at right angles to the magnetic field, the liquid is pumped in a direction normal to both the magnetic field and the direction of current flow. Conversely, if a highly conductive fluid is caused to flow through a magnetic field, current flows through the liquid and a voltage is built up across the liquid in a direction normal to the magnetic field. The present invention utilizes both of these phenomena to provide a direct current transformer.

In its broader aspects, the present invention provides a magnetohydrodynamic transformer comprising means defining a flow path for a conductive fluid, a magnetohydrodynamic pump in the flow path for pumping the conductive fluid, and a magnetohydrodynamic generator in the flow path downstream of the pump for developing an electric potential as the conductive fluid flows through the generator. By varying various parameters in the design of the pump and the generator, the transformer of the invention may be adapted for use as either a voltage transformer or a current transformer, i.e. as either a voltage step-up transformer or a current step-up transformer. Because the resistance of the conductive fluid is extremely low, the transformer has an extremely low impedance. This is particularly desirable when the transformer is used with other devices which have a matching low impedance,

3,179,824 Patented Apr. 20, 1965 "ice such for example, as in solid state thermoelectric generators.

The invention will be better understood by reference to the following description of several embodiments, taken in conjunction with the accompanying drawings, in which:

FIGS. 1, 2 and 3 are diagrammatic perspective views, with parts broken away, of three embodiments of the invention; and

FIG. 4 is a diagrammatic sectional view showing insulating dividers that are useful in all of the embodiments of the invention.

FIG. 1 illustrates diagrammatically an embodiment of the invention adapted for use as a current transformer. A duct 10 of uniform rectangular cross-section and made of a non-conductive material provides a flow path for a conductive fluid (not shown), which may flow in the direction shown by the arrow. Although it is not so shown for reasons of simplicity, the duct 10 in practice may form a closed loop so that the conductive fluid can recirculate continuously. In that case, the direction of flow is immaterial.

A magnetohydrodynamic pump, indicated generally by the numeral 11, is located in the flow path of the conductive fluid, and a magnetohydrodynamic generator, indicated generally by the numeral 12, is also located in the flow path downstream from the generator 11.

The magnetohydrodynamic pump 11 comprises a magnet having pole pieces 13a and 13b, located on opposite sides of the duct 10 for providing magnetic flux across the flow path of the conductive fluid. The pump 11 also includes a pair of electrodes 14a and 14b, which are located inside the duct 10, spaced apart on opposite sides of the flow path. The electrodes 14a, 14b, extend along the flow path and are substantially coextensive in that direction with the magnet pole pieces 13a, 13b. A direct potential source 15 is connected between the electrodes 14a, 14b.

The conductive fluid that is confined within the duct 10 may be any one of several types, and the invention is in no way limited to the use of any particular fluid. Examples of suitable fluids are the liquid forms of mercury, gallium, and sodium, or a suitable electrolyte. Furthermore, the invention also comtemplates the use of a highly conductive hot gas plasma as the conductive fluid. The principal qualification is that the fluid must be highly conductive, so that current may readily flow through the fluid between the electrodes 14a and 14b.

The magnetohydrodynamic generator 12, located downstream of the pump 11, is very similar in construction to the pump 11. It includes a magnet having pole pieces 16:; and 16b located on each side of the duct 10 for providing magnetic flux across the flow path of the conductive fluid. Electrodes 17a and 17b are located inside the duct 10 and are spaced apart on opposite sides of the flow path. The electrodes 17a and 17]) extend along the flow path and, in the case of a current transformer, are spaced closer together than are the electrodes 14a and 14b in the pump 11. In the present instance, that is accomplished by placing the pump electrodes on the sides and the generator electrodes on the top and bottom of the duct. An electrical load, shown as a simple resistor 18, is connected between the electrodes 17a and 17b of the generator 12.

When current from the source 15 flows through the conductive fluid between the electrodes 14a, 14b, normal to the direction of the magnetic field, a physical force is exerted on the fluid which causes it to move or be pumped along the duct 10. The conductive fluid pumped by the pump 11 then flows through the magnetic field between the pole pieces 16a, 16b, in the generator 12, and a voltage is built up normal to the field between the electrodes 17a and 17b. Thus, current flows through the conductive fluid between electrodes 17a, 17b, and through the electrical load 18 connected between the electrodes. The area of the generator electrodes may be selected to provide an internal impedance that is of the same order of magnitude as the impedance of the load 18.

If small flow losses are assumed, it has been found that the following relationship is valid for transformation ratios smaller than 5:1. The relationship is where U and U are the voltages between the electrodes of the pump and generator, respectively; I and I are the currents flowing between the electrodes in the pump and generator, respectively; B and B are the strengths of the magnetic fluxes existing across the flow path in the pump and generator, respectively; and X and X are the distances between the electrodes in the pump and generator, respectively. Thus, it is seen that by making the spacing between the electrodes 17a, 17b, of the generator 12. less than that between the electrodes 14a, 14b in the pump 11, a current transformer is provided, wherein the increase in current is substantially inversely proportional to the spacing between the electrodes in the pump and generator assuming that B and B are equal. Similarly, if the generator electrodes are spaced farther apart than the pump electrodes, a voltage step-up will be obtained. It is pointed out that the current transformer shown in FIG. 1 may be converted to a voltage transformer by interchanging the voltage source 15 and the load 18. Thus the pump and transformer are interchanged.

FIG. 2 illustrates an embodiment of the invention adapted for use as a voltage transformer. It differs from the embodiment shown in FIG. 1 not only in that the electrodes in the magnetohydrodynamic generator section are spaced farther apart than those in the pump section, but also in that the straight duct of uniform cross section has been replaced by a duct 20 having a varying cross section. The duct 20, which may providev a closed flow path for a conductive fluid, includes a pump section 21, an adapter section 22, and a generator section 23. The adapter section 22 serves merely to connect the pump and generator sections 21 and 23 and to reverse the cross-sectional dimensions of the duct between the pump and generator sections.

The pump section 21 of the duct contains a magnetohydrodynamic pump, indicated generally by the numeral 24 and the generator section 23 of the duct contains a magnetohydrodynamic generator, indicated generally by the numeral 25.

The pump 24 differs from the pump 11 (FIG. 1) in that electrodes 26a and 26b are spaced apart across the shorter dimension of the rectangular duct rather than across the longer dimension. Also the magnet pole pieces 27a and 27b that provide flux across the duct at right angles to the direction of flow are smaller than those previously described. Of course, a direct potential source 28 is connected between the electrodes 26a, 26b.

The generator 25 differs from the generator .12 shown in FIG. 1 in several ways. First, because the configuration of the duct has changed, magnet pole pieces 30a and 30b, which provide magnetic flux across the flow path, are considerably larger than those shown in FIG. 1. Also electrodes 31a and 31b, which are located on the top and bottom sides of the duct, are farther apart because of the configuration of the duct. An electrical load, shown as a simple resistor 32, is connected between the electrodes 3 1a and 31b.

In operation, the embodiment of the invention shown in FIG. 2 is very similar to that previously described with reference to FIG. 1. They both operate in accordance with the formula previously set forth. It is pointed out, however, that for a voltage transformer (FIG. 2) the p 5 between the generator electrodes must be greater 4 than that between the pump electrodes or the magnetic flux in the generator must be greater than that in the pump, or both.

The reasons that the electrodes 31a, 31b, in the magnetohydrodynamic generator 25 are smaller in area than are the electrodes in the magnetohydrodynamic pump 24 is to provide an internal impedance between the electrodes 31a, 3112, that is of the same order of magnitude as the electrical load 32 connected between the electrodes.

FIG. 3 illustrates another embodiment of the invention adapted for use as a voltage transformer. The transformer shown in FIG. 3 is very similar to that shown in FIG. 2, and comprises a duct 34 for providing a flow path for a conductive fluid, a magnetohydrodynamic pump 24, and a magnetohydrodynamic generator 25. The pump 24 and the generator 25 may be identical with those previously described bearing the same reference numerals. The duct 30 differs from that shown in FIG. 2 in that it is of uniform cross section and is merely twisted by substantially between the locations of the pump and generator. Thus, it provides the same pump and generator sections shown in FIG. 2 but without the use of an adapter section to interchange the cross-sectional dimensions. Its operation is the same as that of the transformer described with reference to FIG. 2.

In both of the voltage transformer embodiments shown in FIGS. 2 and 3, the flow paths provided by the ducts 20 and 34 may be closed so that the direction of flow of the conductive fluid is unimportant. The voltage sources 15 and 28 may be connected between the pump electrodes with either polarity.

Either of the voltage transformers of FIGS. 2 and 3 may be converted to a current transformer by interchanging the potential source and the electrical load. Thus, the pump becomes a generator, and the generator becomes a pump.

It has been found in practice that using a duct with 20 mm. x 0.5 mm. cross-section, B =B =10,000 gauss, U =.001 v. and 1 :10 amps, one can obtain up to .006 v. across a load of 0.01 ohm.

It has been found that, in the generator stage of the transformer of the invention, the conductive liquid itself provides a return path for the electric current that is generated. Thus, the liquid is effectively connected in parallel with the electrical load and tends to short circuit the load. This effect can be minimized by subdividing the flow path on each side of the generator stage. Such an arrangement is shown in FIG. 4.

The arrangement shown in FIG. 4 may be advantageously applied to any one of the embodiments of the invention previously described. It comprises a plurality of insulating dividers 35 conventionally mounted within a duct 36, which divide the duct into a plurality of horizontal sections. The dividers 35 are substantially parallel and extend in the direction of flow of the conductive fluid, both upstream and downstream from a generator 37. In fact, they may extend substantially from the downstream edge of a pump 38 clear to the upstream edge of the generator 37 and then downstream from the generator for some distance. Thus, the flow of current through the conductive fluid on each side of the generator is substantially reduced because there is no direct path through the fluid on either side of the generator.

Although several embodiments of the transformer of the invention have been described, it is apparent that many modifications and changes may be made by one skilled in the art without departing from the true scope and spirit of the invention.

What is claimed is:

1. A magnetohydrodynamic transformer comprising a nonconductor rectangular duct forming a flow path for a conductive fluid of low resistance; a magnetohydrodynamic pump including magnetic poles located on opposite sides of said duct for providing magnetic flux across said flow path, a first pair of electrodes inside said duct on opposite sides thereof and extending along said flow path substantially coextensive with said magnetic poles, and a direct potential source connected to said first pair of electrodes; a magnetohydrodynamic generator in said flow path downstream of said pump including magnetic pole pieces located on opposite sides of said duct for providing magnetic flux across said flow path, .a second pair of electrodes located inside said duct and extending on opposite sides of said flow path substantially coextensive with said magnetic pole pieces; and an electrical load connected to said second pair of electrodes; said magnetohydrodynamic pump and said magnetohydrodynamic generator having a transformer relationship of where U and U; are the voltages between the first and second pairs of electrodes of said pump and said generator, respectively, 1 and 1 are the currents flowing between the first and second pairs of electrodes of said pump and said generator, respectively, B and B are the strengths of the magnetic flux existing across the flow path in said respective pump and generator, and X and X are the distances between the first and second pairs of electrodes of said pump and said generator, respectively; said distance between said second pair of electrodes in said flow path of said generator being less than said distance between said first pair of electrodes in said flow path of said pump.

2. A magnetohydrodynamic transformer comprising a nonconductor rectangular duct forming a flow path for a conductive fluid of low resistance; a magnetohydrodynamic pump including magnetic poles located on opposite sides of said duct for providing magnetic flux across said flow path, a first pair of electrodes inside said duct on opposite sides thereof and extending along said flow path substantially coextensive with said magnetic poles, and a direct potential source connected to said first pair of electrodes; a magnetohydrodynamic generator in said flow path downstream of said pump including magnetic pole pieces located on opposite sides of said duct for providing magnetic flux across said flow path, a second pair of electrodes located inside said duct and extending on opposite sides of said flow path substantially coextensive with said magnetic pole pieces; and an electrical load connected to said second pair of electrodes; said magnetohydrodynamic pump and said magnetohydrodynamic generator having a transformer relationship of erator, respectively, I and I are the currents flowing between the first and second pairs of electrodes of said pump and said generator, respectively, B and B are the strengths of the magnetic fiux existing across the flow path in said respective pump and generator, and X and X are the distances between the first and second pairs of electrodes of said pump and said generator, respectively; said distance between said second pair of electrodes in said flow path of said generator being greater than said distance between said first pair of electrodes in said flow path of said pump.

3. A magnetohydrodynamic transformer comprising a nonconductor rectangular duct forming a flow path for a conductive fluid of low resistance; a magnetohydrodynamic pump including magnetic poles located on opposite sides of said duct for providing magnetic flux across said flow path, a first pair of electrodes inside said duct on opposite sides thereof, and extending along said flow path substantially coextensive with said magnetic poles, and a direct potential source connected to said first electrodes; a magnetohydrodynamic generator in said flow path downstream of said pump including magnetic pole pieces located on opposite sides of said duct for providing magnetic flux across said flow path, a second pair of electrodes located inside said duct and extending on opposite sides of said flow path substantially coextensive with said magnetic pole pieces; and an electrical load connected to said second pair of electrodes; said magnetohydrodynamic pump and said magnetohydrodynamic gen erator having a transformer relationship of U I B X where U and U are the voltages between the first and second pairs of electrodes of said pump and said generator, respectively, 1 and I are the currents flowing between the first and second pairs of electrodes of said pump and said generator, respectively, B and B are the strengths of the magnetic flux existing across the flow path in said respective pump and generator, and X and X are the distances between the first and second pairs of electrodes of said pump and said generator, respectively; the area of said second electrodes being smaller than the area of said first electrodes; the internal impedance of said generator being substantially the same magnitude as the impedance of said electrical load.

References Cited by the Examiner UNITED STATES PATENTS 1,196,511 8/16 Berger 310-11 3,034,002 5/62 Carlson 3l011 FOREIGN PATENTS 1,121,202 1/62 Germany.

MILTON O. HIRSHFIELD, Primary Examiner.

DAVID X. SLINEY Examiner. 

1. A MAGNETOHYDRODYNAMIC TRANSFORMER COMPRISING A NONCONDUCTOR RECTANGULAR DUCT FORMING A FLOW PATH FOR A CONDUCTIVE FLUID FLOW RESISTANCE; A MAGNETOHYDRODYNAMIC PUMP INCLUDING MAGNETIC POLES LOCATED ON OPPOSITE SIDES OF SAID DUCT OF PROVIDING MAGNETIC FLUX ACROSS SAID FLOW PATH, A FIRST PAIR OF ELECTRODES INSIDE SAID DUCT ON OPPOSITE SIDES THEREOF AND EXTENDING ALONG SAID FLOW PATH SUBSTANTIALLY COEXTENSIVE WITH SAID MAGNETIC POLES, AND A DIRECT POTENTIAL SOURCE CONNECTED TO SAID FIRST PAIR OF ELECTRODES; A MAGNETOHYDRODYNAMIC GENERATOR IN SAID FLOW PATH DOWNSTREAM OF SAID PUMP INCLUDING MAGNETIC POLE PIECES LOCATED ON OPPOSITE SIDES OF SAID DUCT FOR PROVIDING MAGNETIC FLUX ACROSS SAID FLOW PATH, A SECOND PAIR OF ELECTRODES LOCATED INSIDE SAID DUCT AND EXTENDING ON OPPOSITE SIDES OF SAID FLOW PATH SUBSTANTIALLY COEXTENSIVE WITH SAID MAGNETIC POLE PIECES; AND AN ELECTRICAL LOAD CONNECTED TO SAID SECOND PAIR OF ELECTRODS; SAID MAGNETOHYDRODYNAMIC PUMP AND SAID MAGNETOHYDRODYNAMIC GENERATOR HAVING A TRANSFORMER RELATIONSHIP OF 